Brief Answer:
Most of these will be helpful

Detailed Answer:
Hello XXXXXXX

Hemogram including PCV,MCH,MCHC,ESR, WBC count with differential, RBC count platelets all these will be helpful. As through these test we can assess whether there is any anemia or not and if it is there then with the help of MCV,MCH,MCHC and peripheral smear type of anemia can be assessed.
Most of the children in this age suffers from iron deficiency anemia(nutritional). So if Hb is low then with the help of Iron study iron deficiency can be detected.

You can go for urine routine examination as sometimes there can be hidden infection but I won't suggest you to go for stool test if you have to pay (even concessional rate) and he is passing stool normally.

Like this I wont recommend for Chest X ray even if it is free. Because X ray can cause radiation harm and it should not be done if there is no specific indication.

Blood grouping and Rh typing is also needed to know the blood group.Serum calcium level will be helpful to see nutritional calcium and vit D deficiency.

USG abdomen will not help much if there are no abdominal or urinary complaints. But you can go for it as a routine check up as there are no side effects like chest X ray.

Diet councelling is very important for your child as his weight is below the normal limit. He should be at least 12 kg at this age.So it will help in improving calorie and thus growth.

Dental and ophthalmological evaluation will also be helpful.

So as per my suggestion

1)Test needed----- Hemogram,PCV,ESR,RBC,Peripheral smear,S Calcium,Urine
examination

2)Test can be done------WBC count,DC,Stool examination,USG abdomen

3) Test can be done only if specifically indicated-------Chest XRAY

Diet councelling, Ophthalmological consultation,Dental consultation----Needed

Kidney consultation ----If specifically indicated

In addition to this Iron profile if there is anemia and Vit D level if there is hypocalcemia from my side.

I hope this answers your query
Reghards

---